This invention relates to an improved resin composition useful for casting, coating and impregnating operations. More particularly, this invention relates to epoxy-urethane resin compositions and to a method for their preparation.
Urethane-epoxy polymers are known to possess several properties which make them uniquely useful in a number of applications. These materials generally are extremely reactive with curing agents and, when mixed with curing agents, become too viscous too rapidly to be used as practical curable liquids. Further, these multi-component resin mixtures require careful proportioning of two or more co-reactants and curing agents and a rapid and thorough mixing of all components immediately prior to use if full development of resin properties is to be attained.
Relatively stable curable liquid polyurethane-polyexpoxides are also known. One such material, set forth in U.S. Pat. No. 2,830,038, is prepared by reacting a polyalkalene ether glycol with an organic diisocyanate and a compound containing one epoxide and one hydroxyl group to produce a liquid prepolymer having urethane linkages and terminal epoxide groups. The prepolymer is then cured by mixing with polyamine compounds containing 2 or more primary or secondary amine groups per molecule and heating for several hours at elevated temperatures. Similarly, related liquid polyurethane-polyepoxides are known which may be more rapidly cured by the addition of anhydride curing agents followed by heating for short period. These so-called storage-stable, single-component resin systems may be used as casting resins, however, the prolonged cure time and elaborate synthesis steps required for their preparation present significant economic disadvantages, particularly where rapid production of low cost moldings is desired.
In both the two-component and single package systems, the curing reactions of most prior art compositions are generally highly exothermic, and where used in casting applications the consequent heat build-up in thick parts causes warping, unequal shrinkage and stresses in the finished casting.
A liquid epoxy-urethane composition which can be cured rapidly at or near room temperatures without appreciable exotherm would thus be a useful improvement in the casting resin art.